Methylcobalamin

Educational overview

Common as an oral supplement; no FDA-approved methylcobalamin injection was identified, so injectable forms are generally compounded or unapproved.

Methylcobalamin (mecobalamin, methyl-B12) is one of the two coenzyme forms of vitamin B12, the cobalt-containing vitamin required for methionine synthase and, through its partner adenosylcobalamin, for methylmalonyl-CoA mutase. In cells it is the methyl donor that regenerates methionine from homocysteine, which is why it is marketed as an "active" or "pre-methylated" form of B12. Commercial products include oral tablets, sublingual lozenges and sprays, and injectable solutions. Cyanocobalamin, the synthetic form found in most fortified foods, supplements, and approved injections, is converted to methylcobalamin and adenosylcobalamin after absorption, so every form of the vitamin ultimately supplies the same two coenzymes.

The biology of vitamin B12 deficiency is established from decades of human data, and the NIH Office of Dietary Supplements notes that no evidence shows absorption differs by supplement form. A 2015 review concluded that the coenzyme forms are unlikely to be superior to cyanocobalamin or hydroxocobalamin for preventing or treating deficiency, partly because methylcobalamin is less stable and because cells strip the upper ligand from any cobalamin before reusing it. Trials specific to methylcobalamin are mostly small, many from Japan, where mecobalamin is a licensed medicine for peripheral neuropathy and megaloblastic anemia. Findings for neuropathic pain are mixed, and reviewers describe the evidence as preliminary rather than confirmatory.

In the United States, oral and sublingual methylcobalamin are dietary supplements. There is no FDA-approved methylcobalamin injection; the approved vitamin B12 injections are cyanocobalamin and hydroxocobalamin products marketed under approved applications for deficiency caused by malabsorption. A DailyMed listing for a methylcobalamin injection carries the marketing category "unapproved drug other" and states that FDA has not found the product safe and effective. Injectable methylcobalamin sold through wellness clinics is therefore either compounded under state pharmacy rules or unapproved, and in 2015 the FDA warned clinicians about unapproved injectable vitamin products, including methylcobalamin, made by an overseas compounder. The regulatory picture differs abroad, where mecobalamin injection is a prescription medicine in Japan.

Approved cyanocobalamin injections are labelled for controlled room temperature with protection from light. Methylcobalamin is more light-sensitive still, converting toward hydroxocobalamin on exposure, and compounded methylcobalamin vials often carry refrigeration instructions and short beyond-use dates set by the dispensing pharmacy, so the pharmacy label governs. Oral products are stable in the closed container away from heat and moisture. Useful record fields are the form (methyl, cyano, or hydroxo), concentration, route, the pharmacy and lot or beyond-use date for compounded vials, and concurrent metformin or acid-suppressing medicines, which lower B12 absorption. Because serum B12 rises after any injection, a dose log dated against laboratory draws helps a clinician interpret results.

Category

Vitamin B12

Routes represented

Oral / Sublingual / Subcutaneous (SubQ)

Storage context

Follow the product or pharmacy label; requirements vary by route and formulation.